1. Field of the Invention
The present invention relates to a hub assembly for receiving a stylet and, more particularly, to a hub assembly for coupling a stylet handle having corresponding tapered mating surfaces.
2. Description of Related Art
Generally speaking, there are two basic techniques for introducing injectable medicament into the spinal area of a patient. The first, introducing spinal anesthesia into the epidural space, “epidural,” and the second, introducing spinal anesthesia by penetration of the dural membrane into the subarachnoid space, “spinal” or “subarachnoid.” The medicaments can be any type of liquid therapeutic material including antibiotics, steroids and the like, but generally include agents used for anesthesia and analgesia.
Delivery of the medicament into the subarachnoid space requires a penetration depth of several centimeters. Puncture of the skin and dural membrane with a needle may result in tissue coring, which can cause complications due to the presence of the tissue in the subarachnoid. In order to prevent tissue coring, a stylet formed as a solid elongated member is typically inserted within the bore of the needle and extends therein. The needle, with the stylet inserted therein, limits tissue from entering the needle. After insertion of the needle within the patient, the stylet may be partially or completely removed from the bore of the needle.
Typically, the stylet is attached to a stylet handle and the needle is attached to a needle hub. The stylet handle engages the needle hub to allow the stylet to be selectively removed from the bore of the needle during the procedure. One way for attaching the stylet handle to the needle hub is to provide a male, outwardly extending portion on the handle, and a female portion on the needle hub for receiving the male portion. An interference fit is provided between the male portion and the female portion so that a compressive force is imparted on the male portion when the stylet handle and the needle hub are engaged. In this attachment design, the assembly and removal forces of the stylet handle and the needle hub is directly related to the coefficient of friction between the male and female elements and the normal force associated with the interference fit. Also, such designs typically incorporate very small interferences between the parts on the order of 0.001 inch to 0.005 inch. Therefore, small variances in geometry and friction can have a large impact on engagement forces. Additionally, since the resultant assembly of the stylet handle and needle hub are usually stored in a stressed (i.e., engaged) state, the engagement forces change over time due to creep. This change in engagement force over time can prevent the stylet handle from adequately engaging the needle hub. Accordingly, there is a general need for a hub assembly that allows a stylet handle to be selectively coupled to a needle hub such that consistent engagement forces are provided.